In production of an ultra large scale integrated (ULSI) semiconductor device, a processing technique for achieving high density and miniaturization of a semiconductor device is currently being studied and developed. One of the processing techniques, a chemical mechanical polishing (CMP) technique becomes essential in production of semiconductor devices for the smoothening of an interlayer dielectric film, the formation of a shallow trench isolation (STI), and the formation of plugs and embedded metal wirings.
In a conventional production process of semiconductor devices, an inorganic insulation film such as a silicon oxide film is formed through plasma CVD (chemical vapor deposition), low-pressure CVD, etc. A fumed silica-based polishing liquid is commonly studied as a chemical mechanical polishing liquid for use in smoothening of the inorganic insulation film. The fumed silica-based polishing liquid is prepared by adjusting the pH of slurry in which particles obtained through grain growth using a method such as thermal decomposition of silicon tetrachloride are mixed. However, the fumed silica-based polishing liquid still has a technical problem that a polishing speed is low.
Also, in the generation of a design rule of 0.25 μm or later, STI has been used for isolation of devices in an integrated circuit. For STI, CMP technique is used for removal of an excessive silicon oxide film formed on a substrate. In this case, a stopper film with a low polishing speed is formed under the silicon oxide film so as to stop polishing at a given depth. A silicon nitride film or the like is used as the stopper film. Not only to effectively remove the excessive silicon oxide film but also to sufficiently prevent the progress of polishing thereafter, a polishing speed ratio between the silicon oxide film and the stopper film is preferably high. However, a conventional colloidal silica-based polishing liquid has a low polishing speed ratio of about 3 between the silicon oxide film and the stopper film, and thus does not have sufficient properties practically usable for STI.
As a polishing liquid for the surface of a glass such as a photomask and a lens, a cerium oxide polishing liquid containing cerium oxide particles is in use. Since the cerium oxide particles are lower in hardness than silica particles or alumina particles and are less likely to cause a polishing surface to be scratched during polishing, the cerium oxide particles are useful for finishing mirror-surface polishing. Furthermore, the cerium oxide polishing liquid has an advantage that the polishing speed is faster than that of a silica polishing liquid such as a fumed silica- or colloidal silica-based polishing liquid.
As the cerium oxide polishing liquid, Patent Literature 1 below discloses a chemical mechanical polishing liquid for semiconductors using high-purity cerium oxide abrasive particles. Also, Patent Literature 2 below discloses a technique for adding an additive in order to control a polishing speed of a cerium oxide polishing liquid and improve global smoothness.